1. Field of the Invention
The present invention relates generally to dental prosthetics, and more particularly, to intra-oral framework systems and components for implant-supported prosthetic restorations. The invention further relates to methods and apparatus for properly positioning and guiding a drill during dental implant surgery.
2. Description of the Related Art
One of the fastest growing specialties in dentistry is prosthodontics, which is the replacement of missing natural teeth with prosthetic restorations, such as a single tooth, a bridge of several prosthetic teeth, or a denture comprising an arc of prosthetic teeth for an edentulous or partially edentulous patient. The prosthetic restorations are shaped and colored to appear like natural teeth, and are typically supported on dental implants that are surgically secured within the patient's jawbone. Various implant designs are available, such as blades, screws and cylinders, and the implants are generally made of titanium or high titanium alloy.
The conventional surgical procedure for installing one, implant-supported, prosthetic tooth includes drilling a properly positioned hole in the jawbone of the patient, inserting the implant in the hole, and attaching the prosthetic tooth to the implant. In circumstances where two or more implants are installed to support a prosthetic bridge, each implant hole must be angled properly and located the correct distance from adjacent implants and natural teeth to achieve proper alignment and appearance for the prosthetic restoration. Proper implant positioning is also extremely important to ensure that the implant is anchored within sufficient bone structure in the patient's jawbone. Typically, to install an entire upper or lower denture, at least four implant holes are drilled into the upper or lower jawbone.
The most common method for locating a dental implant hole is to visually survey the area and drill the hole in a freehand manner. However, this method can readily result in imperfect bores due to space limitations associated with working inside a patient's mouth. Thus, dental surgeons have encountered difficulty forming implant holes with a sufficient degree of parallelism and proper positioning. A variety of problems can result from flawed or imperfect implant holes, such as uneven force distribution, insufficient bone growth around the implant, secondary infections, and ultimately, implant failure. Therefore, various types of surgical stents and positioning guide systems have been developed to aid the dental surgeon.
A traditional surgical stent is a custom-built template for properly spacing dental implants and for guiding the drill as the implant holes are formed. One exemplary method for making and using a surgical guide stent is described in U.S. Pat. No. 5,556,278 to Meitner, hereby incorporated herein by reference. First, a cast impression is made of the patient's mandible or maxilla jawbone (arch) that includes an edentulous space where one or more implant-supported prosthetic teeth will be installed. A diagnostic tooth set-up formed of wax or other known material is made to fit within the edentulous space of the cast arch. Next, the dental surgeon drills a hole through each diagnostic tooth set-up and into the base of the cast arch. The hole corresponds to the location and orientation of the implant hole in the patient's real arch. Once the hole is drilled in the cast arch, the tooth set-up is removed, a guide post is inserted into each hole, and a guide sleeve is slid over the projecting end of the guide post. A resinous, moldable material is applied on the cast arch around the guide sleeves and cured to form a template. The template with the guide sleeves embedded therein is then removed from the cast arch. When the template is ready for use, the dental surgeon inserts it into the patient's mouth, and the guide sleeves can be radiographically visualized to confirm that they are in the optimum position and orientation before implant holes are drilled therethrough.
Thus, such traditional surgical stents aid the dental surgeon in properly positioning the implant holes, and also guide the drill as the implant holes are being formed. However, because each surgical stent is custom-built, these devices are only useful for a single patient, they are costly to fabricate, and they require a number of intermediary office and laboratory steps to take an impression of the patient's arch and create a cast model from which the surgical stent is formed.
Therefore, to reduce costs and the number of steps associated with fabricating a traditional surgical stent, various forms of prefabricated surgical stents have been developed. One exemplary prefabricated surgical stent is disclosed in U.S. Pat. No. 5,775,900 to Ginsberg et al., hereby incorporated herein by reference, which describes a clear, thermoplastic acrylic resin stent to facilitate visualization of the underlying supporting tissues. A kit is provided to the dental surgeon comprising prefabricated stents of mandibular and/or maxillary arches in small, medium, and large base sizes based on anatomical averages for the population with various tooth arrangements on each base size. For any particular patient, a stent of the appropriate base size is selected and placed in water of 120°–160° F. for approximately 2 minutes, allowing the resin to become moldable. The inner surface of the stent is then molded in the mouth of the patient or on a cast model of the patient's arch to closely approximate the edentulous ridge. Simultaneously, the outer surface of the stent is adjusted to position the prosthetic teeth. Once formed and subsequently cooled, the stent becomes stable and can be placed in the patient's mouth at the time of implant surgery for proper alignment of the implants. Thus prefabricated stents provide some advantages over traditional surgical stents. However, each prefabricated stent is only useful for a single patient.
In addition to surgical stents, prefabricated drill guide systems have been developed. One exemplary drill guide system is disclosed in U.S. Pat. No. 5,636,986 to Pezeshkian, hereby incorporated herein by reference. Pezeshkian describes prefabricated drill guide fixtures comprising interconnected housings configured in the shape of teeth with vertically disposed drill bushings passing therethrough. The drill guide fixtures are provided in different configurations depending on the number of prosthetic teeth that will be installed. For example, a drill guide fixture may comprise three housings fixed together in a size and configuration to resemble three adjacent prosthetic teeth that will be installed as a bridge. A pin is used to position the fixture in an initially drilled hole, and the fixture is rotated about the axis of the pin until the tooth-shaped housings are properly aligned. The dental surgeon then drills through the drill bushings in each housing to form the implant holes. The drill bushings guide the drill and reduce the likelihood of slippage or breakage of the drill bit during drilling. Although the drill guide fixtures are prefabricated and may theoretically be used more than once, dental restorations come in a great variety of configurations. Therefore, the dental surgeon would likely be required to purchase a separate drill guide fixture for each patient to provide the configuration that matches the patient's restoration requirements.
Another exemplary drill guide system is disclosed in U.S. Pat. No. 5,915,962 to Rosenlicht, hereby incorporated herein by reference. Rosenlicht describes a kit comprising a plurality of tooth emulations that differ in size and shape to replicate cuspids, bicuspids, molars, etc. Each tooth emulation includes a pilot guide hole extending along an axis of rotation. The tooth emulations are connected together in an articulated manner for relative movement and relative axial orientation to each other. The dental surgeon connects together a plurality of tooth emulations to form an articulatable model approximating the size and shape of the patient's natural teeth. The model is positioned on the patient's edentulous site, or a cast model thereof, and adjusted as necessary. Then the model is luted or otherwise rigidified to form a rigid guide for drilling implant holes into the patient's jawbone through the pilot guide hole in each emulation. Thus, this drill guide system includes prefabricated tooth emulations that are intended to enable the dental surgeon to build a model that matches the patient's restoration configuration. However, each articulatable model is only useful for one patient.
An alternate type of guide is a drill positioning guide. One exemplary type of drill positioning guide is the Brånemark System offered by Nobelpharma AB. This system includes stainless steel, L-shaped guides, each comprising a vertical pin portion and a horizontal positioning portion. For each guide, the pin has a particular diameter and the positioning portion has a particular lateral length. Once the first implant hole is drilled, the pin is placed inside the hole such that the positioning portion extends horizontally over the gumline to locate the next implant hole. The drill bit is aligned against the end of the positioning portion opposite the pin to drill the adjacent implant hole. Therefore, the lateral length of the positioning portion determines the centerline to centerline distance between adjacent implants to ensure adequate spacing between implants. Further, the height of the positioning portion provides a guide for drilling the depth of the implant hole. In particular, the positioning portion is 8 mm high, and may include notches to indicate each 2 mm increment. The dental surgeon can align depth indicators on the drill bit with either the full height of the positioning portion or the notches on the positioning portion to drill implant holes of approximately equal depth.
Accordingly, the L-shaped-prefabricated positioning pins facilitate spacing between implants and enable the drilling of implant holes having approximately equal depth. These positioning guides may be used more than once for any patient with any restoration configuration. However, these pins do not guide the drill bit to ensure that it remains oriented at the proper angle to drill implant holes having a sufficient degree of parallelism. Therefore, it would be desirable to provide a drill guide system comprising simple, prefabricated components that may be used more than once, for any restoration configuration, that enable precise implant spacing, and also ensure that the implant holes are drilled at the proper angle and orientation.
Employing widely used conventional techniques, once the implants are positioned, they perform no function for one to six months to allow time for the implants to osseointegrate into the patient's jawbone. During this time, the patient wears a temporary, removable denture. Once the osseointegration period is complete, the next step in providing a permanent, multi-unit restoration is to create a framework that is typically custom-fabricated in a laboratory for the individual patient from gold alloy or titanium components. The framework interconnects and joins together the implants, provides a foundation for the prosthetic restoration, and provides an attachment structure for connecting the prosthetic bridge or denture to the multiple implants. Thus, the framework is a permanent structure disposed between the implants and the dental restoration.
The process for creating a custom-fabricated framework is similar to the process for creating a traditional surgical stent. First, a cast impression of the patient's mandible or maxilla jawbone (arch) is taken in the dentist's office, from which a model of the patient's arch is made to indicate the locations of the implants. Using the model, the entire framework is fabricated in a laboratory to precisely fit onto the implants. The prefabricated framework is then transferred to the dental surgeon for positioning onto the actual implants. Although formed using the model, the prefabricated framework may not precisely fit onto the implants, in which case the framework must be adjusted. The adjustment may require that a bar be cut and re-soldered or re-cast, which often must be performed in a laboratory that is located elsewhere. If a minor change is required, the dental surgeon can adjust the framework in the office, but these modifications are typically finalized in the off-premises laboratory. This fitting and adjustment process may go back and forth between the laboratory and the surgeon's office a number of times, thereby increasing the cost, time, and inconvenience to the patient.
Another type of framework system is the laser-welded titanium framework, which does not require laboratory involvement and may be installed as an integral part of the implant surgery to immobilize the implants. The laser-welded framework system allows a dental surgeon to custom build the titanium framework right into the patient's mouth by welding together titanium components using an intra-oral welding machine. Since the framework is built onto the implants in the patient's mouth, a good fit can be ensured. However, the skill required to weld intra-orally limits the widespread application of this type of framework system. Accordingly, it would be desirable to provide a framework system that can be constructed directly onto the actual implants without requiring special skills, such as intra-oral welding.
Audax Dental AG of Basel, Switzerland offers the Connect Bar System comprising a variety of components designed to be positioned to form a framework system in the dentist's office without intra-oral welding. Specifically, the Connect Bar System comprises a Housing Unit, a Bar Unit, and a Bar Sleeve. The Housing Unit includes a bore for receiving a fixation screw, a double-hex (12-sided) recess formed in the base for receiving a hexagonal extension from a non-rotating abutment, and one or two sockets formed into the sides, each socket for receiving a ball head of a Bar Unit. The Bar Unit comprises a straight portion and a ball head formed on one end that is designed to fit into the socket of the Housing Unit. The Bar Sleeve comprises a sleeve designed to fit over the straight portions of two adjacent Bar Units when their straight portions are aligned, end-to-end.
To assemble the Connect Bar System, non-rotational abutments with hexagonal upper extensions are first fit onto the implants. A Housing Unit is then disposed on top of each abutment so that the double-hex recess of the Housing Unit receives the hexagonal upper extension of the abutment, thereby enabling the Housing Unit to be adjusted to one of twelve rotational positions with respect to the implant. A Bar Unit is connected to each Housing Unit by inserting the ball head portion into a socket of the Housing Unit, thereby allowing full rotational movement of the Bar Unit with respect to the Housing Unit. Prior to installation, the Bar Units are cut to the appropriate length as perceived by the dental surgeon. To join adjacent Bar Units and complete a bar assembly that spans between Housing Units, the Bar Sleeve is fit over the ends of adjacent Bar Units.
Thus, the Connect Bar System offers the advantages of providing a framework system consisting of components that may be assembled together and installed directly into the patient's mouth without requiring intra-oral welding. However, the dental surgeon is required to precisely cut the Bar Units to the proper length, which adds to the time required to perform the procedure. Also, three components, namely two Bar Units and a Bar Sleeve, must be interrelated and assembled to form a single bar assembly to span between two Housing Units, thereby adding to the cost and the number of components required for the framework system. Further, the Housing Unit does not connect directly to the implant but instead connects to an intermediary non-rotational abutment, thereby adding another component to the overall prosthetic system. Additionally, the Housing Unit is restricted to one of twelve distinct rotational positions (30° apart) with respect to the implant, rather than having full rotational freedom of movement. Accordingly, it would be desirable to provide a simplified framework system of prefabricated components that did not require adjustment by the dental surgeon, that had full rotational freedom of movement with respect to the implant to maximize adjustability during installation, and that enabled direct connection to the implants to reduce the total number of components in the final restoration.
The present invention overcomes various of the deficiencies of the prior art.